1. Field of the Invention
This invention relates generally to heating and ventilation equipment, and more specifically to vent dampers and flue closures for oil or gas-fired hot water heaters.
2. Description of the Prior Art
Many modern hot water heaters are designed to burn oil or natural gas to generate their heat energy. In these systems, the fuel is burned in a combustion chamber located in or near the base of the heater, and the water contained in the heater is conductively heated through the walls of the heater both by contact with the fire of the combustion itself, as well as by contact with the hot combustion gasses rising through the heater's central core. Because these combustion gasses are toxic, they must be vented to the outside air by means of an exhaust duct or flue.
Energy losses through such exhaust ducts can be significant; it is estimated that approximately 33% of the heat energy generated from the main burner and pilot light operation is lost directly up the flue. In addition, an unrestricted duct allows cool room air to circulate freely through the hot water heater and its central core, thereby cooling the heated water and requiring the main burner to operate more frequently than would otherwise be necessary. Thus, it is clearly desirable, for efficiency and cost considerations, to regulate the flow of gasses both in and out of a gas-fired hot water heater.
Numerous damping devices have been developed for use with boilers, furnaces, and other cumbustion gas-producing systems. Many are simply hinged, one-way mechanical valves that prevent outside air from coming down the exhaust duct. While effective for that purpose, such devices often require significant exhaust flow in order to open, and thus are useable only with relatively large units, or those equipped with a fan or blower. Some large commercial water heaters may include power-assisted or computer-controlled mechanical dampers. Unfortunately, such systems are too costly and cumbersome for widespread domestic use. Still other damping devices utilize bimetal expansion/contraction valves to regulate flow. However, these devices tend to respond slowly to temperature and flow changes.